final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 42
and the risks of fast-moving traffic hitting falsework
are becoming more acute. These longer spans have
resulted in more complex systems of falsework.
Such systems require considerable experience and
skill to erect. By requiring the work to be supervised
by a Iicensed engineer the contractors are being
forced to recognise the level of professional skill
required.
Mr Elliott made these points:
"From a design standpoint, insofar as possible and
especially over traffic, designs are avoided that would
leave heavy loads on falsework for any extended
period - for instance supporting precast beams until
they can be cast into caps. Now enough of the cap is
cast to support the beams adequately, then an additional pour is made to grout in the ends of the beams.
Where possible, falsework is avoided over traffic,
railroad or highway. Precast members can be used to
achieve this - up to spans of 120ft (37 m). The
highway division is also designing bolster hinges into
some post-tensioned concrete box girder overpasses
that will eliminate heavy falsework bents (that is
supports) at hinge points. In post-tensioning spans,
bolsters bear against the opposing hinge diaphragms
to carry stressing loads directly into the bridge
structure. This also allows the contractor to use
lighter weight steel scaffolding.
The contractor is required to have his falsework designed by a licensed engineer. If possible, the engineer's
responsibility should also be extended to the erection
of the falsework. Of course, the falsework built must
correspond with the design.
The falsework plans are carefully checked by the
State engineers.
The constructed falsework is carefully checked for
joint fits, bracing, stiffness, overturning possibilities,
foundation settlement and general adequacy. These
checks must continue immediately prior to and during
the concrete placing.
Requirements are set up for the top and bottom
anchorage and the protection of falsework posts
which are adjacent to traffic. Generous traffic openings
are required. Warning devices, collision walls and
guard rails are required.
The above view is that of a highly regarded highway
engineer in the United States and the practices of his
administration are reinforced by legal sanction. An
engineer is required to satisfy the requirements of
.. The Professional Engineers' Act" before he can be
granted the certificate which allows him to practise
rofessionally. A certificate to practise in one State
oes not confer the automatic right to practise in
other. It is further enacted that "it is unlawful for
one other than a professional engineer registered
under this Act to stamp or seal any plans, specifications etc with the seal or stamp of a professional
engineer or consulting engineer unless registered under
that Act".
Subsidiary legislation promulgated by the Division of
Industrial Safety in the State of California lays down
its own requirements on falsework and vertical
shoring. Amongst other requirements under Article
1717 of the appropriate Order it is laid down that an
engineer who is registered as a civil engineer in the
State of California must approve and sign for the
detailed design calculations and working drawings for
all falsework where the height of the falsework (as
measured from the top of the sill to the soffit of the
superstructure) exceeds 14 feet, or where the length
of an individual span exceeds 60 feet, or where provision is made for vehicular or railroad traffic through
the falsework.
Further, such falsework is required to be inspected
prior to the placement of concrete by an engineer
registered as a civil engineer in the State of California
who shall certify in writing that the falsework substantially conforms to the working drawings and that
the material and workmanship are satisfactory for the
purpose intended. A copy of this certificate is required
to be available at the site of the work at all times.
Canada
The regularisation of falsework procedures in Canada
was stimulated by the collapse of the Second Narrows
Bridge in 1958, and again by the Heron Road Bridge
falsework failure in 1966. The Canadian falsework
procedures vary from province to province. In Ontario
for example the relevant legislation is the Construction
Safety Act, 1973 and in British Columbia the legislation was made under the Workmen's Compensation
Board of British Columbia and became effective on
1 May 1972. In essence the legislation requires that all
design drawings of falsework in specified categories
shall be checked and sealed by a professional engineer
and additionally sealed by an independent professional
engineer. The latter must satisfy the terms of the
province registration authority and is referred to as
the proof engineer.
In Ontario S. 142(4) lays down that if falsework
includes any of the following features:
(a) tubular metal frames;
(b) columns where the effective length is dependent
upon the provision of lateral restraints between the
ends of the columns;
(c) shores placed one upon another to form a supporting system that is more than one tier in height;
43
